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    <title>arhnk</title>
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    <center>Scilab Function</center>
    <div align="right">Last update : April 1993</div>
    <p>
      <b>arhnk</b> -  Hankel norm approximant</p>
    <h3>
      <font color="blue">Calling Sequence</font>
    </h3>
    <dl>
      <dd>
        <tt>[slm]=arhnk(sl,ord,[tol])     </tt>
      </dd>
    </dl>
    <h3>
      <font color="blue">Parameters</font>
    </h3>
    <ul>
      <li>
        <tt>
          <b>sl</b>
        </tt>: linear system (<tt>
          <b>syslin</b>
        </tt> list)</li>
      <li>
        <tt>
          <b>ord</b>
        </tt>: integer, order of the approximant</li>
      <li>
        <tt>
          <b>tol</b>
        </tt>: threshold for rank determination in <tt>
          <b>equil1</b>
        </tt>
      </li>
    </ul>
    <h3>
      <font color="blue">Description</font>
    </h3>
    <p>
    computes <tt>
        <b>slm</b>
      </tt>, the optimal Hankel norm approximant of the 
    stable continuous-time linear system <tt>
        <b>sl</b>
      </tt> with matrices <tt>
        <b>[A,B,C,D]</b>
      </tt>.</p>
    <h3>
      <font color="blue">Examples</font>
    </h3>
    <pre>

A=diag([-1,-2,-3,-4,-5]);B=rand(5,1);C=rand(1,5);
sl=syslin('c',A,B,C);
slapprox=arhnk(sl,2);
[nk,W]=hankelsv(sl);nk
[nkred,Wred]=hankelsv(slapprox);nkred
 
  </pre>
    <h3>
      <font color="blue">See Also</font>
    </h3>
    <p>
      <a href="equil.htm">
        <tt>
          <b>equil</b>
        </tt>
      </a>,&nbsp;&nbsp;<a href="equil1.htm">
        <tt>
          <b>equil1</b>
        </tt>
      </a>,&nbsp;&nbsp;<a href="../robust/hankelsv.htm">
        <tt>
          <b>hankelsv</b>
        </tt>
      </a>,&nbsp;&nbsp;</p>
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